The membrane of a cell serves the vital function of partitioning the molecular contents from its external environment. The membranes are largely composed of amphiphilic lipids, which self-assemble into highly insulating structures and thus present a large energy barrier to trans-membrane ionic transport.
However, the lipid matrix can be disrupted by a strong external electric field leading to an increase in trans-membrane conductivity and diffusive permeability, a well-known phenomenon known as electroporation. These effects are the result of formation of aqueous pores in the membrane. More particularly, electroporation process involve permeation of cell membranes upon application of short duration electric field pulses, traditionally between relatively large plate electrodes (Neumann, et al., Bioelectrochem Bioenerg 48, 3-16 (1999); Ho, et al., Crit Rev Biotechnol 16, 349-62 (1996)).
For example, FIGS. 2A and 2B show a conventional electroporation system 20, whereby impression of an electric field (e.g., shown by closing a circuit 22) creates random pores 26 in a cell membrane 24. The distribution of such pores, in terms of size and number only, is determined by the strength and duration of the applied electric field. The stronger and the longer the electric field is applied, the more numerous and larger the pores are. However, the exact location of such pores cannot be controlled, and thus the final distribution of pores is somewhat random. Researchers lose control over where compounds are introduced into the intracellular matrix, an oft-important ingredient in biochemical pathways. Thus researchers often have to rely on the cell's own natural mechanisms, a far slower and difficult process to utilize.
Electroporation is used for introducing macromolecules, including DNA, RNA, dyes, proteins and various chemical agents, into cells. Large external electric fields induce high trans-membrane potentials leading to the formation of pores (e.g., having diameters in the range of 20-120 nm). During the application of the electric pulse, charged macromolecules, including DNA, are actively transported by electrophoresis across the cell membrane through these pores (Neumann, et al., Biophys J 712 868-77 (1996)). Uncharged molecules may also enter through the pores by passive diffusion. Upon pulse termination, pores reseal over hundreds of milliseconds as measured by recovery of normal membrane conductance values (Ho, 1996, supra).
This procedure is often used in laboratory settings to inject chemical and biological compounds into a cell, avoiding the reliance on the cell's own protein receptors and trans-membrane channels for transport across the cell membrane. This allows researchers to easily study the biological affect of compounds, be it a potentially life-saving cancer drug or a deadly biological toxin. However, current electroporation techniques are limited.
Therefore, it would be desirable to provide a method and system to overcome these and other limitations of conventional electroporation.